Patent GB-787795-A (GB)
Title: Improvements in gas turbine fuel systems
IPC: F02C7/26
Filed: 1956-05-14
Abstract: 787,795. Gas turbine plant; gear pumps. GENERAL MOTORS CORPORATION. May 14, 1956 [May 26, 1955], No. 14906/56. Classes 110 (2) and 110 (3). A gas turbine fuel system in which a pump delivers an excess supply of fuel to a regulating apparatus which supplies a metered proportion to the engine and returns the surplus to the pump inlet has a valve operable to render the regulating apparatus ineffective so that the whole of the pump delivery is passed to the engine, which valve is operated on a given engine speed being reached during starting and rendered inoperative again by a given fuel pressure being reached so as to restore the effectiveness of the regulating apparatus. Fuel is supplied to the gas turbine manifold 13 by a booster pump 23, a main positive displacement pump 24, preferably a gear pump, and an auxiliary fuel pump 26 of the same type as the main pump but of slightly smaller capacity. The discharge of pump 23 is connected directly to the inlet of pump 26 and to the inlet of pump 24 through a check-valve 29. Pump 24 discharges through a filter 32 to the fuel delivery line 37 which is also connected to the discharge of pump 26 through a filter 33 and check valve 38. A normally open valve 39 is connected between the filter 33 and the inlet of the main pump 24. In normal operation the valve 39 is open and pump 24 satisfies the engine requirements. Pump 26 then runs unloaded. If pump 24 should partially or completely fail, pump 26 develops pressure, closing check valve 29 and opening check valve 38. The auxiliary pump 26 then supplies the engine. The bellows 43 then close a switch 44 to energize a signal light 46. By energizing the solenoid 41 and closing the valve 39 the two pumps are put in parallel and the full discharge of both pumps fed to the fuel line 37. The fuel is metered by the control 50 which discharges through a shut-off valve 52 and an engine temperature control 53 to the fuel manifold 13. The excess fuel is returned to the pump inlet from the main control through a conduit 54 and from the temperature control through a conduit 56. A by-pass 68 provided with a normally closed valve 67 is provided around the main control 50. Before starting the engine the bus-bar is energized which causes current to flow through back contacts 75a of a speed switch 75 and normally closed pressure-operated switch 79 to a relay 82. This relay closes the holding contacts 82b which by-pass the back contacts 75a. The starting of the engine is initiated by energizing the starter 18 with the fuel shut-off valve 52 closed, the ignition generator 16 inoperative, the valve 67 closed and the valve 39 open so that the pump 24 is operative and the pump 26 inoperative. At a predetermined engine speed the speed switch 75 closes front contacts 75a and opens back contacts 75a. This causes the motor 70 to open the shut-off valve 52. Back contacts 75b remain closed so that relay 88 is energized. This relay closes contacts 88a so that the operating solenoid 41 of the valve 39, the ignition generator 16 and the drain valve solenoid 66 are all energized. Valve 39 is then closed so that the pumps 24, 26 operate in parallel and the drain valve 64 closed. At the same time, the valve 67 is opened by energization of the solenoid 69 through the contacts 82a. When a predetermined pressure is reached in the fuel delivery line, the pressure switch 79 opens and breaks the holding circuit for the relay 82. The front contacts 82a are then opened, which causes the valve 67 to be closed. At the self-sustaining speed of the engine, the speed switch 75 opens the back contacts 75b which causes the valve 39 to be opened, the ignition 16 to be cut off and the solenoid 66 to be de-energized. The drain valve 64 remains closed under the manifold pressure. The valve 67 may be arranged in the by-pass 54 downstream of the main control 50 only or downstream of the main and temperature controls.